Method and apparatus for supporting CSG service in wireless communication system

ABSTRACT

A method and apparatus for supporting a closed subscriber group (CSG) service is provided. A user equipment determines whether a neighbor cell is a CSG member cell for which a CSG whitelist includes a CSG identity of the neighbor cell and PLMN identities of the neighbor cell. The user equipment sends a CSG membership indicator indicating whether the neighbor cell is the CSG member cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/635,762, filed on Mar. 2, 2015, now U.S. Pat. No. 9,319,947, which isa continuation of U.S. patent application Ser. No. 14/471,872, filed onAug. 28, 2014, now U.S. Pat. No. 9,008,667, which is a continuation ofU.S. patent application Ser. No. 13/585,559, filed on Aug. 14, 2012, nowU.S. Pat. No. 8,848,592, which claims the benefit of U.S. ProvisionalPatent Application No. 61/523,830, filed on Aug. 15, 2011, the contentsof which are all hereby incorporated by reference herein in theirentirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for supporting a closedsubscriber group (CSG) service in a wireless communication system.

Related Art

The Third Generation Partnership Project (3GPP) Long Term Evolution(3GPP LTE) which is a set of enhancements to the Universal MobileTelecommunications System (UMTS) is introduced as 3GPP Release 8. The3GPP LTE uses orthogonal frequency division multiple access (OFDMA) forthe downlink, and single carrier frequency division multiple access(SC-FDMA) for the uplink, and adopts multiple input multiple output(MIMO) with up to 4 antennas. Research is now underway on 3GPPLTE-Advanced (LTE-A), which is a major enhancement to 3GPP LTE.

Closed subscriber group (CSG) services, which are services that can beprovided only to a certain group of subscribers, have been introduced toimprove quality of service. A base station (BS) capable of providing CSGservices is referred to as a Home eNodeB (HNB), and a cell serving CSGmembers is referred to as a CSG cell. The basic requirements regardingCSG services are as disclosed in 3GPP TS 22.220 V1.0.1 (2008-12)“Service requirements for Home NodeBs and Home eNodeBs (Release 9)”.

Given that most CSG services are provided at higher costs than othertypical wireless communication services, it is important to guaranteethe quality of CSG services.

There is a need for a method and apparatus to improve the quality of CSGservices.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for supporting aclosed subscriber group (CSG) service in a wireless communicationsystem.

The present invention also provides a method and apparatus for providingCSG subscription information in a wireless communication system.

In an aspect, a method for supporting a closed subscriber group (CSG)service in a wireless communication system is provided. The methodincludes receiving, by user equipment, from a serving cell, a CSGrequest for CSG subscription of a neighbor cell, receiving, by the userequipment, cell information broadcast by the neighbor cell, the cellinformation including a CSG identity of the neighbor cell, a firstPublic Land Mobile Network (PLMN) identity and at least one second PLMNidentity, determining, by the user equipment, whether the neighbor cellis a CSG member cell for which a CSG whitelist of the user equipmentincludes the CSG identity and one of the first PLMN identity and the atleast one second PLMN identity, and reporting, by the user equipment, tothe serving cell, CSG subscription information, the CSG subscriptioninformation including the CSG identity of the neighbor cell and a CSGmembership indicator indicating whether the neighbor cell is the CSGmember cell.

The CSG request may be associated with a handover to the neighbor cell.

In another aspect, a user equipment configured for supporting a closedsubscriber group (CSG) service in a wireless communication system isprovided. The user equipment includes a memory configured to store a CSGwhitelist of the user equipment, and a processor operatively coupled tothe memory and configured to receive, from a serving cell, a CSG requestfor CSG subscription of a neighbor cell, receive cell informationbroadcast by the neighbor cell, the cell information including a CSGidentity of the neighbor cell, a first Public Land Mobile Network (PLMN)identity and at least one second PLMN identity, determine whether theneighbor cell is a CSG member cell for which the CSG whitelist of theuser equipment includes the CSG identity and one of the first PLMNidentity and the at least one second PLMN identity, and report, to theserving cell, CSG subscription information, the CSG subscriptioninformation including the CSG identity of the neighbor cell and a CSGmembership indicator indicating whether the neighbor cell is the CSGmember cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a mobile communication system to which thepresent invention are applied.

FIG. 2 is a block diagram showing radio protocol architecture for a userplane.

FIG. 3 is a block diagram showing radio protocol architecture for acontrol plane.

FIG. 4 is an exemplary view illustrating a network architecture formanaging an HNB by using an HNB gateway.

FIG. 5 is a flowchart illustrating a method of checking the access modeof a base station by the UE.

FIG. 6 is a flowchart illustrating a handover to a CSG cell. The sourcecell can be a CSG cell or non-CSG cell. The target cell can be a CSGcell.

FIG. 7 is a flowchart illustrating a method for reporting CSGsubscription information.

FIG. 8 is a flowchart illustrating a method for supporting CSG serviceaccording to an embodiment of the present invention.

FIG. 9 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a view illustrating a mobile communication system to which thepresent invention are applied. This system may be also referred to as anEvolved-UMTS Terrestrial Radio Access Network (E-UTRAN) or a Long TermEvolution (LTE)/LTE-advanced (LTE-A) system.

The E-UTRAN includes at least one base station (BS) 20 providing a userplane and a control plane towards a user equipment (UE) 10. The UE canbe fixed or mobile and can be referred to as another terminology, suchas a MS (Mobile Station), a UT (User Terminal), a SS (SubscriberStation), MT (mobile terminal), a wireless device, or the like. The BS20 may be a fixed station that communicates with the UE 10 and can bereferred to as another terminology, such as an e-NB (evolved-NodeB), aBTS (Base Transceiver System), an access point, or the like.

The BSs 20 are interconnected with each other by means of an X2interface. The BSs 20 are also connected by means of the S1 interface tothe EPC (Evolved Packet Core) 30, more specifically to the MobilityManagement Entity (MME) by means of the S1-MME and to the ServingGateway (S-GW) by means of the S1-U.

The EPC 30 may include the MME, the S-GW, and a Packet DataNetwork-Gateway (P-GW). The MME has information on the connection of UEor the capability of UE, and such information is primarily used for themobility management of the UE. The S-GW is a gateway having E-UTRAN asan end point, and the P-GW is a gateway having PDN as an end point.

The radio interface protocol layers between UE and a network can bedivided into a first layer (L1), a second layer (L2) and a third layer(L3) based on three lower layers of an Open System Interconnection (OSI)reference model widely known in communications systems. A physical layerbelonging to the first layer provides information transfer servicesusing a physical channel, and a radio resource control (RRC) layerlocated at the third layer plays a role of controlling radio resourcesbetween UE and a network. For the purpose of this, the RRC layerexchanges RRC messages between UE and a network.

FIG. 2 is a block diagram showing radio protocol architecture for a userplane. FIG. 3 is a block diagram showing radio protocol architecture fora control plane. The data plane is a protocol stack for user datatransmission and the control plane is a protocol stack for controlsignal transmission.

Referring to FIGS. 2 and 3, a physical (PHY) layer provides informationtransfer services to upper layers on a physical channel. The PHY layeris coupled with a MAC (Medium Access Control) layer, i.e., an upperlayer of the PHY layer, through transport channels. Data is transferredbetween the MAC layer and the PHY layer through the transport channel.The transport channels are classified by how and with whatcharacteristics data are transferred over the radio interface.

Between different physical layers, i.e., the physical layer of atransmitter and the physical layer of a receiver, data are transferredthrough the physical channel. The physical channel may be modulated byan Orthogonal Frequency Division Multiplexing (OFDM) scheme, and timeand frequency are used as radio resources for the physical channel.

The functions of the MAC layer include mapping between logical channelsand transport channels, and multiplexing/demultiplexing of MAC SDUs(Service Data Units) belonging to one or different logical channelsinto/from transport blocks (TBs) delivered to/from the PHY layer ontransport channels. The MAC layer provides services to a RLC (Radio LinkControl) layer through logical channels.

The functions of the RLC layer include concatenation, segmentation andreassembly of RLC SDUs. In order to guarantee various quality ofservices (QoSs) required by radio bearers (RBs), the RLC layer providesthree operating modes: TM (Transparent Mode), UM (Unacknowledged Mode)and AM (Acknowledged Mode). The AM RLC provides error correction throughautomatic repeat request (ARQ).

The functions of a Packet Data Convergence Protocol (PDCP) layer for theuser plane include transfer of user data, headercompression/decompression and ciphering/deciphering. The functions ofthe PDCP layer for the control plane include transfer of control planedata, and ciphering and integrity protection.

A Radio Resource Control (RRC) layer is defined only in the controlplane. The RRC layer serves to control the logical channels, thetransport channels and the physical channels in association withconfiguration, reconfiguration and release of radio bearers (RBs). A RBmeans a logical path provided by a first layer (i.e. PHY layer) andsecond layers (i.e. MAC layer, RLC layer and PDCP layer) for datatransmission between a UE and a network. Configuring the RB includesdefining radio protocol layers and characteristics of channels toprovide a service and defining specific parameters and operationschemes. The RB may be classified into a signaling RB (SRB) and a dataRB (DRB). The SRB is used as the path to transfer RRC messages in thecontrol plane and the DRB is used as the path to transfer user data inthe user plane.

If an RRC connection is established between a RRC layer of the UE and aRRC layer of the E-UTRAN, then the UE is in an RRC_CONNECTED state.Otherwise, the UE is in an RRC_IDLE state.

Downlink transport channels for transmitting data from a network to UEmay include a Broadcast Channel (BCH) for transmitting systeminformation, and a downlink Shared Channel (SCH) for transmitting otheruser traffic or control messages. In case of traffic or control messagesof a downlink multicast or broadcast service, they may be transmittedeither via a downlink SCH, or via a separate downlink Multicast Channel(MCH). On the other hand, uplink transport channels for transmittingdata from UE to a network may include a Random Access Channel (RACH) fortransmitting an initial control message and an uplink Shared Channel(SCH) for transmitting user traffic or control messages.

Logical channels which are located at an upper level of transportchannels and mapped to the transport channels may include a BroadcastControl Channel (BCCH), a Paging Control Channel (PCCH), a CommonControl Channel (CCCH), a Multicast Control Channel (MCCH), a MulticastTraffic Channel (MTCH), and the like.

A physical channel includes multiple symbols inn time domain andmultiple sub-carriers in frequency domain. A sub-frame includes aplurality of symbols in the time domain. A sub-frame includes aplurality of resource blocks each including a plurality of symbols and aplurality of sub-carriers. Also, each sub-frame can use particularsub-carriers of particular symbols (e.g., a first symbol) in therelevant sub-frame for a Physical Downlink Control Channel (PDCCH), thatis, a L1/L2 control channel. A Transmission Time Interval (TTI) as aunit time for transmitting data is 1 ms, corresponding to one sub-frame.

Hereinafter, an RRC state and an RRC connection method of UE will bedescribed in detail.

The RRC state refers to whether or not the RRC layer of the UE islogically connected to the RRC layer of the E-UTRAN. If connected, thenit is called an RRC_CONNECTED state, and otherwise it is called anRRC_IDLE state. For the UE in an RRC_CONNECTED state, the E-UTRAN canrecognize the existence of the relevant UE in a cell unit because thereexist an RRC connection thereof, and thus the E-UTRAN can effectivelycontrol the UE. On the contrary, for the UE in RRC_IDLE state, theE-UTRAN cannot recognize the relevant UE, and therefore, it is managedby a core network in a tracking area unit, which is a unit larger than acell. In other words, the existence of the UE in an RRC_IDLE state isonly recognized in a large area unit, and therefore, it should bechanged to an RRC_CONNECTED state in order to receive typical mobilecommunication services such as voice or data.

When the UE is initially turned on by a user, the UE first searches fora suitable cell and then is camped in an RRC_IDLE state in thecorresponding cell. The UE camped in an RRC_IDLE state makes an RRCconnection with the E-UTRAN through an RRC connection procedure when itis required to make an RRC connection, thereby changing the state to anRRC_CONNECTED state. There are several cases when the UE in the RRC_IDLEstate is required to make an RRC connection. For example, an uplink datatransmission may be required due to a phone call attempt by the user, orthe like, or the transmission of a response message may be required inresponse to a paging message received from the E-UTRAN.

A Non-Access Stratum (NAS) layer belonging to the upper layer of the RRClayer serves to perform session management and mobility management.

In order to manage the mobility of the UE at the NAS layer, both an EPSMobility Management-REGISTERED (EMM-REGISTERED) state and anEMM-DEREGISTERED state are defined, and both states will be applied tothe UE and the MME. The UE is initially in an EMM-DEREGISTERED state,and carries out a process of registering it into the correspondingnetwork through an ‘Initial Attach’ procedure in order to access anetwork. If this ‘Attach’ procedure has been successfully carried out,then the UE and the MME will be in an EMM-REGISTERED state.

In order to manage a signaling connection between the UE and the EPC,both an EPS Connection Management (ECM)-IDLE state and an ECM-CONNECTEDstate are defined, and the both states will be applied to the UE and theMME. If the UE in an ECM-IDLE state makes an RRC connection withE-UTRAN, then it will be in an ECM-CONNECTED state. If the MME in anECM-IDLE state makes an S1 connection with E-UTRAN, then it will be inan ECM-CONNECTED state. When the UE is in an ECM-IDLE state, the E-UTRANhas no context information of the UE. Therefore, the UE in an ECM-IDLEstate carries out a UE-based mobility procedure such as a cell selectionor cell reselection without receiving a command from the network. On thecontrary, when the UE is in an ECM-CONNECTED state, the mobility of theUE is managed by a command of the network. If the location of the UE inan ECM-IDLE state is changed from the location that has been recognizedby the network, the UE performs a Tracking Area Update procedure tonotify the network of the corresponding location of the UE.

A Public Land Mobile Network (PLMN) is a network deployed and operatedby mobile network operator(s). Each mobile network operator runs one ormore PLMNs. Each PLMN can be identified with the Mobile Country Code(MCC) and the Mobile Network Code (MNC). The PLMN information of a cellis broadcast in the system information. When UE is powered on, PLMNselection is triggered. For the selected PLMN, UE attempts to registerthe selected PLMN. If the registration is successful, the selected PLMNbecomes a registered PLMN (RPLMN). Network can signal to the UE a listof PLMN for which the UE considers those PLMNs in the PLMN listequivalent to its RPLMN. The PLMN equivalent to RPLMN is called as anequivalent PLMN (EPLMN). The UE that registered with network should bereachable by the network at any time. If the UE is in a ECM-CONNECTED(equivalently RRC_CONNECTED), the network is aware of the cell the UE isbeing served. However, while the UE is in a ECM-IDLE (equivalentlyRRC_IDLE), the context of the UE is not available at the BS but storedin the MME. In this case, the location of the UE in ECM-IDLE is onlyknown to the MME at the granularity of a list of Tracking Area (TA)s. Asingle TA is identified by the Tracking Area Identity (TAI) whichconsists of the PLMN Identity the tracking area belongs to and theTracking Area Code (TAC) that uniquely represents the TA in the PLMN.

Network services provided to UE can be divided into three types asfollows. Furthermore, the UE may recognize the type of a celldifferently based on which service can be received. First, the type ofservices will be described, and then the type of a cell will bedescribed below.

1) Limited service: This service provides an emergency call and anearthquake and tsunami warning system (ETWS), and may be provided in anacceptable cell.

2) Normal service: This service denotes a public use with generalpurposes, and may be provided in a suitable or normal cell.

3) Operator service: This service denotes a service for communicationnetwork service providers, and this cell can be only used bycommunication network service providers but cannot be used by typicalusers.

With regard to the service types provided by a cell, the type of a cellcan be divided as follows.

1) Acceptable cell: A cell in which the UE can receive a limitedservice. This cell is not barred and satisfies the cell selectioncriteria of the UE from a standpoint of the corresponding UE.

2) Suitable cell: A cell in which the UE can receive a normal service.This cell satisfies the condition of an acceptable cell, and at the sametime satisfies additional conditions. For additional conditions, thecell should be attached to PLMN to which the corresponding UE can beaccessed, and it should be a cell in which the implementation of atracking area update procedure by the UE is not barred. If the relevant(or corresponding) cell is a CSG cell, then it should be a cell that canbe accessed by the UE as a CSG member.

3) Barred cell: A cell broadcasting information that it is a barred cellthrough the system information.

4) Reserved cell: A cell broadcasting that it is a reserved cell throughthe system information.

Hereinafter, Closed Subscriber Group (CSG) will be described.

A base station which provides CSG service is called a Home Node B (HNB)or Home eNB (HeNB) in 3GPP. Hereinafter, both the HNB and HeNB arecommonly designated as a HNB. An object of the HNB is basically toprovide specialized services only to a member of the CSG. However, thoseservices may be provided to other users in addition to the CSG dependingon the operation mode setting of the HNB.

FIG. 4 is an exemplary view illustrating a network architecture formanaging an HNB by using an HNB gateway (GW).

HNBs may be connected to EPC via HNB GW or directly connected to EPC.Here, the HNB GW is regarded as a typical BS to MME. Also, the HNB GW isregarded as the MME to the HNB. Therefore, an S1 interface is connectedbetween HNB and HNB GW, and also an S1 interface is connected betweenthe HNB GW and the EPC. Furthermore, even in case of directly connectingbetween HNB and EPC, it is connected via an S1 interface. The functionof HNB is almost similar to the function of a typical BS.

In general, HNB has a low radio transmission output power compared tothe BS owned by mobile communication service providers. Therefore, theservice coverage provided by HNB is typically smaller than the servicecoverage provided by (e)NB. Due to such characteristics, the cellprovided by HNB is classified as a femto cell in contrast to a macrocell provided by (e)NB from a standpoint of the service coverage.

From a standpoint of provided services, when HNB provides those servicesonly to a CSG group, the cell provided by this HNB is referred to as aCSG cell.

Each CSG has its own identifier which is called a CSG ID (CSG identity).The UE may have a CSG list to which the UE itself belongs as a memberthereof, and this CSG list may be changed by a request of the UE or acommand of the network. In the current specification of the 3GPP, oneHNB may support one CSG

A UE has a list of CSGs to which the UE belongs as a member. This listis called as a CSG white list.

HNB delivers the CSG ID of the CSG being supported by itself through thesystem information, thereby allowing only the corresponding CSG memberUE to be accessed. When a CSG cell is found by the UE, what CSG beingsupported by this CSG cell can be checked by reading the CSG ID includedin the system information. The UE that has read the CSG ID regards thecorresponding cell as an accessible cell only if the UE itself is amember of the corresponding CSG cell or the CSG corresponding to the CSGID is included in the UE's CSG white list.

It is not always required for HNB to allow only the CSG UE to beaccessed. Based on the configuration setting of HNB, non-CSG member UEmay be allowed to be accessed. The type of UE allowed to be accessed maybe changed based on the configuration setting of HNB. Here, theconfiguration setting denotes the setting of the access mode (or may becalled as operation mode) of HNB. The access mode of HNB can be dividedinto three types as follows based on the type of UE.

1) Closed access mode: A mode in which services are provided toparticular CSG members only. A CSG cell is provided by the HNB.

2) Open access mode: A mode in which services are provided without anyrestriction of particular CSG members like typical (e)NB. The HNBprovides a typical cell not a CSG cell. For clarity, a macro cell is acell operated by the open access mode.

3) Hybrid access mode: A mode in which CSG services are provided toparticular CSG members and also services are provided to non-CSG memberslike a typical cell. It is recognized as a CSG cell for the CSG memberUE, and recognized as a typical cell for the non-CSG member UE. Thiscell is called a hybrid cell.

HNB notifies the UE that the cell being serviced by itself is a CSG cellor typical cell, allowing the UE to know whether or not it can beaccessed to the corresponding cell. HNB being managed in a closed accessmode broadcasts via the system information that it is a CSG cell. Inthis manner, HNB allows the system information to include a CSGindicator indicating whether or not the cell being serviced by itself isa CSG cell in the system information.

For example, the CSG cell broadcasts by setting the CSG indicator to‘TRUE’. If the cell being serviced is not a CSG cell, then it may beused a method that the CSG indicator may be set to ‘FALSE’ or thetransmission of the CSG indicator is omitted. The UE should distinguisha typical cell from a CSG cell, and thus a typical BS may also transmitthe CSG indicator (for example, the CSG indicator set to ‘FALSE’),thereby allowing the UE to know that the cell type provided by itself isa typical cell. Furthermore, the typical BS may not transmit the CSGindicator, thereby allowing the UE to know that the cell type providedby itself is a typical cell, too.

The CSG-related parameters transmitted by the corresponding cell foreach cell type are represented in Table 1. The CSG-related parametersmay be transmitted via system information.

TABLE 1 CSG Cell Typical Cell CSG Indicator ‘CSG Cell’ is indicated‘Non-CSG cell’ is indicated, or not transmitted CSG ID Supported CSG IDis transmitted Not transmitted

The types of UE allowed to be accessed for each cell type arerepresented in Table 2.

TABLE 2 CSG Cell Typical Cell UE not supporting CSG Access denied Accessaccepted Non-CSG member UE Access denied Access accepted CSG member UEAccess accepted Access accepted

FIG. 5 is a flowchart illustrating a method of checking the access modeof a base station by the UE.

A UE checks a CSG indicator in system information of a target cell inorder to confirm what is the type of the target cell (S510).

After checking the CSG indicator, if the CSG indicator indicates thatthe target cell is a CSG cell, then the UE recognizes the correspondingcell as the CSG cell (S520, S530). The UE checks the CSG ID in thesystem information in order to check whether or not the UE itself is aCSG member of the target cell (S540).

If it is checked from the CSG ID that the UE is a CSG member of thetarget cell, then the corresponding cell will be recognized as anaccessible CSG cell (S550, S560). If it is checked from the CSG ID thatthe UE is not a CSG member of the target cell, then the correspondingcell will be recognized as an inaccessible CSG cell (S550, S570).

If the CSG indicator indicates that the target cell is not a CSG cell,then the UE recognizes the target cell as a typical cell (S520, S580).Furthermore, if the CSG indicator is not transmitted in the step S510,the UE recognizes the object cell as a typical cell.

In general, CSG cells and macro cells may be concurrently managed in aparticular frequency. A CSG dedicated frequency is a frequency in whichCSG cells exist only. A mixed carrier frequency is a frequency in whichCSG cells and macro cells exist. The network may reserve a physicallayer cell identifier for the CSG cell in a mixed carrier frequency. Thephysical layer cell identifier is called a Physical Cell Identity (PCI)in E-UTRAN, and called a Physical Scrambling Code (PSC) in UTRAN. Forclarity, the physical layer cell identifier will be expressed by PCI.

The CSG cell notifies information on the PCI reserved for CSG cell at acurrent frequency via the system information. The UE received thisinformation can determine whether or not this cell is a CSG cell fromthe PCI of the cell when a certain cell is found at the correspondingfrequency. How this information being used by the UE will be illustratedbelow in case of two types of UE.

First, in case of the UE, not supporting the CSG-related function orhaving no CSG list to which the UE itself belongs, the UE does not needto regard a CSG cell as a selectable cell during the cellselection/reselection process or handover. In this case, the UE checksonly the PCI of the cell, and then the UE may immediately eliminate thecorresponding cell during the cell selection/reselection process orhandover if the PCI is a reserved PCI for CSG. Typically, the PCI of acertain cell may be immediately known during a process of checking theexistence of the corresponding cell in a physical layer by the UE.

Second, in case of the UE having a CSG list to which the UE itselfbelongs, when the UE wants to know a list of the neighboring CSG cellsat a mixed carrier frequency it may be known that the corresponding cellis a CSG cell if only a cell having the PCI reserved for CSG is found,instead of individually checking the CSG identity of the systeminformation of every cell found in the whole PCI range.

Hereinafter, handover to CSG cell will be described in detail.

While the UE is in RRC_CONNECTED state, the UE performs normalmeasurement and mobility procedures based on configuration provided bythe network. Handover to a CSG cell is different from the normalhandover procedure in three aspects:

(1) Proximity Estimation: in case the UE is able to determine, usingautonomous search procedures, that it is near a CSG cell or hybrid cellwhose CSG ID is in the UE's CSG whitelist, the UE may provide to thesource BS an indication of proximity.

(2) PSC/PCI Confusion: due to the typical cell size of HNBs being muchsmaller than macro cells, there can be multiple HNBs within the coverageof the source BS that have the same PSC/PCI. This leads to a conditionreferred to as PSC/PCI confusion, wherein the source BS is unable todetermine the correct target cell for handover from the PSC/PCI includedin the measurement reports from the UE. PSC/PCI confusion is solved bythe UE reporting the global cell identity of the target HNB.

(3) Access Control: if the target cell is a hybrid cell, prioritizationof allocated resources may be performed based on the UE's membershipstatus. Access control is done by a two step process, where first the UEreports the membership status based on the CSG ID received from thetarget cell and the UE's CSG whitelist, and then the network verifiesthe reported status.

FIG. 6 is a flowchart illustrating a handover to a CSG cell. The sourcecell can be a CSG cell or non-CSG cell. The target cell can be a CSGcell.

A source cell in which the UE is currently camping configures the UEwith a proximity indication control (S611).

The UE sends an “entering” proximity indication when it determines itmay be near a cell (based on autonomous search procedures) whose CSG IDis in the UE's CSG whitelist (S612). The proximity indication includesthe RAT and frequency of the cell.

After sending an “entering” proximity indication, if the UE determinesthat it is no longer near a cell whose CSG ID is in the UE's CSGwhitelist, the UE sends a “leaving” proximity indication to the sourcecell. Upon reception of this indication, the source cell may reconfigurethe UE to stop measurements on the reported RAT and frequency.

If a measurement configuration is not present for the concernedfrequency/RAT the source cell configures the UE with relevantmeasurement configuration including measurement gaps as needed, so thatthe UE can perform measurements on the reported RAT and frequency(S613). The network may also use the proximity indication to minimizethe requesting of handover preparation information of CSG/hybrid cellsby avoiding requesting such information when the UE is not in thegeographical area where cells whose CSG IDs are in the UEs CSGWhite-list are located.

The UE sends a measurement report including the PCI (S621).

The source cell configures the UE to perform SI acquisition andreporting of a particular PCI (S622).

The UE performs SI acquisition using autonomous gaps, i.e., the UE maysuspend reception and transmission with the source cell within aspecific limit to acquire the relevant system information from thetarget cell (S623).

The UE sends a measurement report including CSG ID and a membershipstatus (S624). The membership status indicates whether the UE is amember of the CSG cell.

The source cell includes the CSG ID in the Handover Required messagesent to a MME (S631).

The MME performs UE access control to the CSG cell based on the CSG IDreceived in the Handover Required message and the stored CSGsubscription data for the UE (S632). If the access control procedurefails, the MME ends the handover procedure by replying with the HandoverPreparation Failure message. If the Cell Access Mode is present, the MMEdetermines the CSG Membership Status of the UE handing over to the CSGcell and includes it in the Handover Request message.

The MME sends the Handover Request message to the target cell includingthe target CSG ID received in the Handover Required message (S633).

The target cell verifies that the CSG ID received in the HandoverRequest message matches the CSG ID broadcast in the target cell and ifsuch validation is successful it allocates appropriate resources (S634).UE prioritisation may also be applied if the CSG Membership Statusindicates that the UE is a member.

The target cell sends the Handover Request Acknowledge message to theMME via the HNB GW if present (S635).

The MME sends the Handover Command message to the source cell (S636).

The source cell transmits the Handover Command (i.e., RRC ConnectionReconfiguration message including mobility control information) to theUE (S637).

In the above procedure, steps S612 and S613 may not be performed in casethe UE has not previously visited the HNB, e.g., when the UE firstvisits a hybrid cell.

The PCI confusion is resolved by steps S622, S623 and S624. The sourcecell can request SI acquisition and reporting for any PCI, not limitedto PSCs/PCIs of CSG or hybrid cells.

To identify a target cell for handover, the serving cell may request theUE to report CSG subscription information.

FIG. 7 is a flowchart illustrating a method for reporting CSGsubscription information.

A UE receives a CSG request from a serving cell (S710). The CSG requestmay request the UE to report CSG subscription of a neighbor cell.

The UE receives system information broadcast by the neighbor cell(S720). Based on the system information, the UE acquires a PCI, a globalcell identity, a tracking area code (TAC) and a CSG ID (S725). Theglobal cell identity may include an identity of RPLMN of the neighborcell and the cell identity of the neighbor cell.

The UE performs CSG membership verification (S730). Based on CSG ID, theUE determines whether the UE is a CSG member of the neighbor cell. If aCSG whitelist of the UE includes the CSG ID, the UE is the CSG member ofthe neighbor cell.

Assuming that the CSG whitelist of the UE does not include the CSG ID atthe RPLMN of the neighbor cell, the UE is not the CSG member of theneighbor cell.

The UE sends to the serving cell a CSG membership status indicating thatthe UE is not the CSG member of the neighbor cell (S740).

Since the UE is not the CSG member of the neighbor cell, the servingcell does not trigger the handover to the neighbor cell (S750).

In general, one base station belongs to one PLMN (i.e. RPLMN). However,in order to facilitate network installation and achieve cost reduction,a plurality of service providers may share one base station. This iscalled as RAN sharing. The cell may broadcast additional PLMN identitiesassociated with all shared service providers. The additional PLMNidentities includes multiple PLMN identities, which may include aprimary PLMN identity and one or more secondary PLMN identity. Theprimary PLMN identity may include a PLMN identity of RPLMN or EPLMN. Thesecondary PLMN identity may include a PLMN identity of EPLMN or RPLMN.According to the CSG subscription reporting of FIG. 7, the UE cannotsupport the RAN sharing since the UE does not consider the additionalPLMN identities to determine the CSG membership status.

FIG. 8 is a flowchart illustrating a method for supporting CSG serviceaccording to an embodiment of the present invention.

A UE receives a CSG request from a serving cell (S810). The purpose ofthe CSG request may be associated with a handover to a neighbor cell.The neighbor cell is a CSG cell and belongs to a plurality of PLMNs. Forexemplary purpose only, it is assumed that there are three PLMNidentities, i.e. one first PLMN identity for RPLMN A and two second PLMNidentities for EPLMN B and C.

The UE receives cell information (i.e. system information) broadcast bythe neighbor cell (S820). Based on the cell information, the UE mayacquire a PCI, a list of PLMN identities, a tracking area code (TAC) anda CSG ID (S825). The list of PLMN identities may include PLMN identitiesfor RPLMN A, EPLMN B and EPLMN C. A primary PLMN identity includes afirst PLMN identity of the list of PLMN identities. Secondary PLMNidentities includes PLMN identities following the primary PLMN identityin the list of PLMN identities. The UE may acquire a global cellidentity as combination of the primary PLMN identity and a cell identitythat uniquely identifies the neighbor cell within the primary PLMN.

The UE performs CSG membership verification (S830). The UE maydetermines whether the neighbor cell is a CSG member cell or not. A CSGwhitelist includes at least one pair of CSG ID and PLMN identity. i.e.{CSG ID_1, PLMN ID_1}, {CSG ID_2, PLMN ID_2}, . . . , {CSG ID_N, PLMNID_N}, where CSG ID_n denotes CSG ID for PLMN identity corresponding toPLMN_ID_n. The neighbor cell is the CSG member cell if CSG ID of theneighbor cell and one PLMN identity in the list of PLMN identities areincluded in the CSG whitelist. For example, when the CSG whitelistincludes {CSG ID of the neighbor cell, PLMN C}, the neighbor cell is aCSG member cell of the UE.

To support inter-PLMN CSG mobility, the UE acquires all PLMN identitiesof the concerned cell that is shared by multiple PLMNs, to examinewhether there is a PLMN to which access is allowed. The UE may acquireadditional PLMN IDs when the serving cell requests CSG information forhandover.

The UE reports CSG subscription information to the serving cell (S840).The CSG subscription information may include the global cell identity,the TAC, the CSG ID and a CSG membership indicator. When the neighborcell is a CSG member cell of the UE, the CSG membership indicator set to‘member’ may be included in the CSG subscription information. The CSGmembership may not be included or the CSG membership indicator set to‘non-member’ may be included in the CSG subscription information if theneighbor cell is not the CSG member cell.

If the neighbor cell is the CSG member cell of the UE, the serving celltransfers the received CSG subscription information to MME, and MMEperforms access verification. If the access verification is successful,the MME will perform handover preparation with the neighbor cell (S850).Then the neighbor cell sends a handover command to the source cell.

If it is determined as the handover to the neighbor cell, the servingcell may send a handover command to the UE (S860).

The UE may perform the handover to the neighbor cell (S870).

The UE can perform handover to a CSG cell which supports multiple PLMNs.

FIG. 9 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

A BS 50 may include a processor 51, a memory 52 and a radio frequency(RF) unit 53. The memory 52 is operatively coupled with the processor 51and stores a variety of information to operate the processor 51. The RFunit 53 is operatively coupled with the processor 11, and transmitsand/or receives a radio signal. The processor 51 may be configured toimplement proposed functions, procedures and/or methods described inthis description. Layers of the radio interface protocol may beimplemented in the processor 51. The processor 51 may implementoperations of the serving cell or the neighbor cell in an embodiment ofFIG. 8.

A UE 60 may include a processor 61, a memory 62 and a RF unit 63. Thememory 62 is operatively coupled with the processor 61 and stores avariety of information to operate the processor 61. The memory mayinclude a CSG whitelist. The RF unit 63 is operatively coupled with theprocessor 61, and transmits and/or receives a radio signal. Theprocessor 61 may be configured to implement proposed functions,procedures and/or methods described in this description. The processor61 may implement operations of the UE in an embodiment of FIG. 8.

The processors 51, 61 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 52, 62 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 53, 63 may include baseband circuitryto process radio frequency signals. When the embodiments are implementedin software, the techniques described herein can be implemented withmodules (e.g., procedures, functions, and so on) that perform thefunctions described herein. The modules can be stored in memories 52, 62and executed by processors 51, 61. The memories 52, 62 can beimplemented within the processors 51, 61 or external to the processors51, 61 in which case those can be communicatively coupled to theprocessors 51, 61 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope of the present disclosure.

What is claimed is:
 1. A method for supporting a closed subscriber group(CSG) service in a wireless communication system, the method performedby a user equipment (UE) and comprising: determining whether a CSGidentity is broadcasted from a neighbor cell; determining whethermultiple Public Land Mobile Network (PLMN) identities are broadcastedfrom the neighbor cell; determining whether the UE is a CSG member ofthe neighbor cell based on at least one of the multiple PLMN identities,if the CSG identity is broadcasted; setting a CSG member status field toa “member”, if the UE is the CSG member; and reporting a measurementreport including the CSG member status field and the CSG identity of theneighbor cell.
 2. The method of claim 1, further comprising: receiving,by the UE from the serving cell, a request for the measurement report.3. The method of claim 2, wherein the request for the measurement reportis associated with a handover of the UE from the serving cell to theneighbor cell.
 4. The method of claim 1, wherein the multiple PLMNidentities include a first PLMN identity and at least one second PLMNidentity of the neighbor cell.
 5. The method of claim 4, furthercomprising: determining that the UE is a CSG member when a CSG whitelistof the UE includes the CSG identity and one of the first and second PLMNidentities.
 6. The method of claim 4, wherein the first PLMN identityidentifies a registered PLMN of the UE and the at least one second PLMNidentity identifies an equivalent PLMN of the UE.
 7. The method of claim4, wherein the first PLMN identity identifies an equivalent PLMN of theUE and the at least one second PLMN identity identifies a registeredPLMN of the UE.
 8. A user equipment (UE) configured for supporting aclosed subscriber group (CSG) service in a wireless communicationsystem, the UE comprising: a memory configured to store a CSG whitelistof the UE; and a processor operatively coupled to the memory andconfigured to: determine whether a CSG identity is broadcasted from aneighbor cell; determine whether multiple Public Land Mobile Network(PLMN) identities are broadcasted from the neighbor cell; determinewhether the UE is a CSG member of the neighbor cell based on at leastone of the multiple PLMN identities, if the CSG identity is broadcasted;set a CSG member status field to a “member”, if the UE is the CSGmember; and report a measurement report including the CSG member statusfield and the CSG identity of the neighbor cell.
 9. The UE of claim 8,wherein the processor is further configured to: receive, from theserving cell, a request for the measurement report.
 10. The UE of claim9, wherein the request for the measurement report is associated with ahandover of the UE from the serving cell to the neighbor cell.
 11. TheUE of claim 8, wherein the multiple PLMN identities include a first PLMNidentity and at least one second PLMN identity of the neighbor cell. 12.The UE of claim 11, wherein the processor is further configured to:determine that the UE is a CSG member when a CSG whitelist of the UEincludes the CSG identity and one of the first and second PLMNidentities.
 13. The UE of claim 11, wherein the first PLMN identityidentifies a registered PLMN of the UE and the at least one second PLMNidentity identifies an equivalent PLMN of the UE.
 14. The UE of claim11, wherein the first PLMN identity identifies an equivalent PLMN of theUE and the at least one second PLMN identity identifies a registeredPLMN of the UE.